I first made a "water column" out of thin acrylic, then foamed over that. I painted it with the rock-looking spraypaint then did a clear coat over that. Didn't work so hot. I'd recommend some sort of epoxy covering instead. The best part is that the heater and UV are completely hidden (last pic), and it's a great place for me to add dry ferts without worrying about a fish taking a big mouthful.

The land part is eggcrate covered in great stuff and silicone. There's a little lake the waterfall drops into and then a little stream to the main area of the tank. They have slate on the bottom. After construction I also added those slate chips to the waterfall itself...else the water just kind of runs down the foam. It looks much cooler cascading over the pieces of slate.

Oh and the return pipe is PVC built into the foam, with a sponge-covered intake on the bottom of the tank, and a 90° flared barb at the top to slide the hose on.